1. Field of the Invention
The present invention relates to image pickup apparatuses and methods for controlling the image pickup apparatuses. In particular, the present invention relates to an image pickup apparatus and a method for controlling the image pickup apparatus for returning a movable portion to a reset position.
2. Description of the Related Art
There are several techniques for leading movable portions to their reset positions, in which movable portions are returned to the reset positions by performing returning operations. The reset positions are specified by origin points (reference points for positioning) which are automatically detected.
Examples of such techniques for detecting an origin point include a “grouping” technique which uses a mechanical end and a technique which uses a reset sensor for origin point detection such as an optical sensor, a magnetic sensor, and a limit switch.
The “grouping” technique is advantageous in miniaturization and cost reduction, since it basically uses only a driving mechanism and a detection system. However, the technique cannot always be employed due to mechanical restrictions caused by “adhesion”. On the other hand, in order to employ a reset sensor, a space is necessary for installing the reset sensor. However, the maximum amount of movement necessary for origin point detection can be reduced by selecting an install position for the sensor, as compared to the “grouping” technique. Therefore, reset sensors are advantageous in terms of speed of leading movable portions to their origin points.
In consumer video lens devices or the like, such reset sensors for returning lenses to their reset positions are used with a view to miniaturization. At the same time, in such consumer vireo lens devices, it is necessary that lenses be returned to their reset positions with high precision and speed. When a speed-reduction mechanism such as a feed screw for preventing a movable portion from being back-driven is used for a driving system of a lens device, a starting position is set in advance near an origin point detection element i.e., a reset sensor so that a returning operation can be performed with high speed. However, when a direct drive mechanism such as a DC linear motor is used, the position of the movable portion is moved by inertia or external force without a locking mechanism installed separately, which causes difficulty in achieving an advantage of high speed returning operation.
In addition, when a non-contact optical sensor or magnetic sensor is used as the reset sensor, a detection error caused by a drive condition of the lens under which the origin point is detected prevents an increase in the speed of returning operation. Such a detection error includes mechanical hysteresis and play between a drive system and a detection system, and response characteristics/hysteresis of the detection system.
There are several techniques for handling such error factors, in which driving velocities and directions are controlled. For example, in a known technique, the direction in which a movable portion passes over a reset sensor is limited to a predetermined direction so that mechanical play and hysteresis in a drive system and hysteresis in a detection system can be handled. In addition, in this technique, for handling response characteristics of the detection system, the velocity at which the movable portion passes over the reset sensor is limited below a predetermined velocity (see, for example, Japanese Unexamined Patent Application Publication No. 2001-87989).
However, the technique for controlling a driving velocity and direction in origin point detection described above may cause a situation where the detection needs to be repeated in a specific direction or where low-speed driving cannot be avoided. This prevents the benefits of a direct drive mechanism from being realized. In addition, increasing precision in installing a reset sensor or enhancing the response characteristics of a detection system disadvantageously results in increased manufacturing cost.
The present invention has been made in view of the above circumstances. Accordingly, there is a need for an image pickup apparatus and a method for controlling the image pickup apparatus which permits detection of an origin point and a returning operation with high seed and precision.